This invention relates to a gasoline vapor recovery system and method and, more particularly, to such a system and method for controlling the flow of vapor from a container as it is being filled with gasoline.
The need for controlling the flow of vapor from a container, such as a vehicle tank, as it receives gasoline is well known. For example, a number of systems and methods have been proposed for controlling the flow of a mixture of air and hydrocarbon vapors (hereinafter referred to as "vapor/air mixture") displaced from a vehicle tank during refueling of the vehicle at a service station, or the like.
Previous gasoline dispensing and vapor recovery systems and methods of this type have included a plurality of dispensing nozzles at each dispensing area of the dispensing, or service, station, with each nozzle being adapted to dispense a different grade of gasoline. Passages are provided in each nozzle for collecting the vapor/air mixture from the fuel tank, and a return line communicates the vapor/air mixture passage for delivering the collected vapor/air mixture to the underground fuel storage tank. Although these designs have been generally successful in recovering a portion of the vapor/air mixture, they are not without problems.
For example, some of the earlier systems and methods relied solely upon vapor/air mixture pressure within the fuel tank to force the vapor/air mixture through the vapor/air mixture return line. However, due to pressure losses and partial obstructions in the vapor/air mixture recovery line (sometimes caused by fuel splashback or condensation), the vapor/air mixture pressure developed in the vehicle fuel tank was often insufficient to force the vapor/air mixture out of the vehicle tank and to the underground storage tank.
Other, more recent, vapor recovery systems employ a vacuum pump for drawing the vapor/air mixture from the vehicle tank and through a vapor/air mixture return line. To avoid the expense of a separate vacuum pump at each dispensing station, such systems have typically resorted to a powerful, continuously-operating vacuum pump and a complicated arrangement of electrically actuated valves for connecting the various vapor/air mixture return lines to the vacuum pump when the various pumps were actuated for dispensing. Acceptance of these designs has been minimal because of the expense and difficulty of both installation and maintenance. Additionally, since they typically draw such a large volume of ambient air relative to the volume of fuel vapor/air mixture, there is a danger of an explosive mixture being formed.
Also, it has been suggested that each dispensing unit include a vacuum pump driven by the dispensing unit's conventional gasoline flow meter and connected to a vapor/air mixture return line. However, this type of apparatus is limited to a linear relationship between gas flow and vapor/air mixture flow, which relationship is not always optimum, since the vapor/air mixture concentration in the return line is dependent on several parameters such as nozzle design, vehicle fill pipe design, weather conditions, wind, vehicle fuel tank temperature, fuel temperature, atmospheric pressure, etc. In apparatus designed to correct for this, a valve has been provided which is controlled by electronics that respond to the gasoline and the vapor/air mixture flow and establish an optimum relationship therebetween. However, this requires a metering device and a control valve for each dispensing nozzle, which is expensive and results in an unduly complicated apparatus. Moreover, in the latter arrangements, the vapor/air mixture metering device is disposed downstream of its associated control valve. Therefore, when the vapor/air mixture expands after leaving the control valve, it causes the operation of the metering device to be less than optimum.
These problems are compounded when the vehicle to be filled with gasoline has a system for removing the gasoline vapors from the vapor/air mixture during the fuel dispensing and vapor recovery operation. These systems are often referred to as "onboard refueling vapor recovery systems" and include a carbon canister, or similar device, through which the vapor/air mixture is passed, for purifying the mixture and venting it through a special vent line. However, since the vapor recovery system of the dispensing station is activated during the gasoline dispensing operation, atmospheric air is often drawn into the nozzle and passed to the gasoline underground storage tank. This causes undesirable pressurization of the tank as well as fugitive emissions both of which lowers the efficiency of the system.